1. Field of the Invention
The present invention relates to golf balls. More particularly, the present invention relates to golf balls having a core and a cover, with dimples being formed on the cover.
2. Description of the Related Art
General golf balls that are commercially available in the market have a core and a cover. The core is composed of a solid rubber, and the cover is composed of a resin composition. There also exist cores composed of two or more layers, as well as covers composed of two or more layers.
There are numerous dimples formed on the surface the cover. A role of the dimples involves causing turbulent flow separation through disrupting the air flow around the golf ball during the flight (hereinafter, referred to as “dimple effect”). By causing the turbulent flow separation, a separating point of air from the golf ball shifts backwards leading to the reduction of a drag coefficient (Cd). The turbulent flow separation promotes the differentia between upper and lower separating points of the golf ball that result from the backspin, thereby enhancing the lift force that acts upon the golf ball. Flight distance of the golf ball is prolonged on behalf of the reduced drag and enhanced lift force. Aerodynamically excellent dimples promote the turbulent flow separation. In other words, aerodynamically excellent dimples may render the air flow better.
During the flight of a golf ball, the air flows along the dimples. Shape of the dimple is one of the important factors that determine the aerodynamic characteristics of the golf ball. In an attempt to improve the dimple effect, a variety of proposals have been made in connection with a cross sectional shape of the dimple. JP-A No. 2-68077 discloses dimples having a protrusion at the center. U.S. Pat. No. 5,735,757 discloses dimples having two curved faces. The curvatures of the faces are different from each other.
Volume of the dimples is also one of the important factors that determine aerodynamic characteristics of the golf ball. U.S. Pat. No. 4,813,677 discloses a golf ball having an index of the dimple volume within a predetermined range.
What are most demanded for a golf ball by golf players are flight performances. In particular, golf players with less power desire golf balls that are excellent in flight performances. There is still left room for improvement of dimples in light of the flight performance. An object of the present invention is to provide a golf ball that achieves a great flight distance upon hitting by even a golf player with less power.